1. Field of the Invention
The present invention relates to electronic apparatuses, such as personal computers, and more particularly, to an electronic apparatus having speaker units for sound reproduction therein.
2. Description of the Related Art
Portable electronic apparatuses that are represented by notebook-sized portable computers and mobile communication equipments, such as the one described in U.S. Pat. No. 5,682,290, comprise a casing and a speaker unit for sound reproduction in the casing. Recently, chances of reproducing music or watching images, such as movies, by portable electronic apparatuses have been increasing with the advance of CD drives, DVD drives, etc. Accordingly, there is a demand for the development of high-performance built-in speaker units that ensure high tone quality.
A modern speaker unit disclosed in U.S. Pat. No. 5,610,992 is a so-called bass-reflex speaker unit that has high bass reproducing capability. In general, the bass-reflex speaker unit has an independent speaker box, i.e., a cabinet, a speaker attached to the front face of the cabinet, a port for bass reflex, and a duct or acoustic tube. The port opens in the front face of the cabinet. The acoustic tube communicates with the port and is located in the cabinet. A sound that is radiated from the back of the speaker into the cabinet is partially emitted from the port in phase with a sound that is radiated from the front face of the speaker. Thus, the bass range can be enhanced to reproduce rich low-pitched sounds or voices.
If the speaker unit constructed in this manner is incorporated in a portable computer, for example, the whole cabinet is located in the casing of the computer. The outer surface of the casing is provided with an opening that faces the speaker of the speaker unit and an opening that faces the bass-reflex port. Those parts of the cabinet which are provided individually with the speaker and the port are exposed to the outside through the openings in the casing of the computer, and partially form the outer surface of the casing.
If the bass-reflex speaker unit is thus incorporated in the electronic apparatus, the speaker and the bass-reflex port are exposed outward from the casing of the electronic apparatus. In designing the speaker unit, therefore, the layout of the port and the duct that extends from the port is restricted inevitably. Since those parts of the cabinet which are provided individually with the speaker and the port partially form the outer surface of the casing of the electronic apparatus, moreover, the shape of the cabinet and the like are restricted. Thus, it is hard and takes a lot of time to develop cabinets that fit electronic apparatuses.
Normally, a pair of speaker units are arranged bilaterally. In order to enjoy high bass-range tone quality, the respective cabinets of the two speaker units should preferably have an ideal volume. However, various electronic components are arranged in the casing of a modern electronic apparatus, and the setting space for the speaker units is limited. In some cases, therefore, it is hard to design the bilateral cabinets with the same volume. If the paired cabinets have different volumes, low-pitched sounds that are outputted from the opposite sides are unbalanced and offensive to the ear.